A liquid crystal polyester resin which exhibits crystallinity while melting is used for various applications and various fields, since it has excellent heat resistance and workability. A liquid crystal polyester can be obtained, for example, by polycondensation of an aromatic hydroxy carboxylic acid, an aromatic diol, an aromatic dicarboxylic acid and derivatives such as an ester compound thereof, which are monomers corresponding to repeating units.
In the polycondensation reaction, in the case of using a compound having a phenolic hydroxyl group as a reaction group, such as a hydroxy carboxylic acid and an aromatic diol, the reactivity is low, and it is difficult for the reaction conversion rate to rise. Therefore, in the case that such compounds are used as a starting material (raw material), a production method in which, in order to increase the reactivity, phenolic hydroxyl groups of these compounds are reacted with fatty acid anhydrides to acylate phenolic hydroxyl groups of these compounds, and then polycondensation of acylated compounds is conducted, has been known. In addition, in order to shorten the reaction time, a reaction conducted in the presence of a catalyst has been explored (see, for example, Patent Documents 1 and 2).
In addition, in order to increase the molecular weight of the liquid crystal polyester, in the case that a polymer is exposed to a high-temperature environment for a long period of time, it is easy for thermal degradation thereof to proceed. For this problem, in a method described in Patent Document 3, polycondensation is conducted in a reaction vessel in a short period of time at first, and then the resulting polymer is pulled out in melting condition while it can be easily pulled out from the reaction vessel, followed by solidification and crush thereof, and then solid phase reaction is conducted to increase the molecular weight of the resulting polymer up to a desired molecular weight. Thus, increasing the molecular weight and improving the productivity of a liquid crystal polyester can be achieved while reducing the thermal history.